This invention relates to a device for tightening threaded joints in two subsequent steps, namely a first step during which a joint is tightened to a predetermined torque snug level and a second step during which the joint is further tightened up to a final predetermined pretension level.
The main purpose of the invention is to accomplish a device by which a threaded joint is tightened up to a predetermined pretension level during a second tightening step and by which the stiffness that varies from joint to joint is prevented from causing an undesirable scattering of the obtained pretension level.
By controlling the rotation speed of the tightening tool it is possible to obtain a tightening process which is advantageous also from the ergonomic point of view. The device according to the invention is particularly intended for manually supported tightening tools by which the tiring and uncomfortable jerks normally occurring during the tightening process are eliminated.
The optimum torque speed growth from the ergonomic point of view depends on several parameters such as
1. The strength of the operator. PA1 2. The operator's ability to react fast. PA1 3. The torque level. PA1 4. The torque snug level, if used. PA1 5. The operator's work position. PA1 6. The shut-off speed.
Since there are several parameters involved, it is realized that from the ergonomic point of view it is important to be able to adjust the speed for obtaining a favorable reaction torque characteristic.
The device according to the invention will be described in further detail below with reference to the drawings.